This invention relates to a heavy duty pneumatic radial tire to be used under high inner pressure and heavy load. In particular it relates to a pneumatic radial tire for an aircraft, which is able to prevent damage of the tire resulting from external cuts in a tread of the tire.
Tread surfaces of pneumatic tires are often cut by stones and metal pieces dispersed on roads when the tires run thereon. With pneumatic tires adapted to be used for light loads as in passenger cars, even if the tires are cut to certain extends, they are scarcely burst due to cuts in treads of the tires because the conditions of use are not severe. However, with pneumatic tires used under conditions of high inner pressure, heavy load and high speed as in aircraft, external cuts in treads immediately result in a burst of the tires.
In general, bias tires are used for aircraft for the following reason. As the carcass is bias and includes many ply layers, it is possible to arrange on radially inner side of a tread a crown protective layer having a plurality of plies including organic fiber cords intersecting with each other. Therefore, even if the tread is externally cut by foreign pieces on a road surface, any enlargement of cuts in the tread is effectively prevented between the crown protective layer and the carcass plies.
On the other hand, pneumatic radial tires having carcasses of plies including radially arranged cords are unsuitable for aircraft for the following reason. As the carcass includes only a few plies and belt layers include circumferential belt layers, even if a crown protective layer having intersecting layers of organic fiber cords is provided, the tire is unable to prevent enlargement of external cuts in treads under severe condition in an aircraft.
A radial tire for an aircraft is disclosed in United States Patent Specification No. 4,402,356 which discloses a feature of using wave-form steel cords for protecting a crown.
When the wave-form steel cords are used in crown protective layers, it is possible to prevent development of external cuts in treads. However, as there is a great difference in rigidity between the crown protective layer and belt layers, cracks would occur between the crown protective layer and belt layers in the event that the tire is subjected to heavy load as in landing of an aircraft or going over protrusions on roads.